The invention relates generally to filter cartridges for filter vessels in fluid purification systems, and more particularly to coupling devices that connect replaceable filter cartridges to outlet tubes in filter vessels for purification of radioactive or other hazardous fluids.
Power plants and other facilities with fluid purification processes frequently have filter tanks or filter vessels to purify a variety of different liquids or gases, such as fluid fossil fuels, or radioactive steam or water at nuclear power plants. Known filter vessels have an inlet supplying a fluid to a main filtration chamber holding a number of tubular filters. Long tubes support and act as the core for the tubular filters. These long tubes extend from a tube sheet that separates the main chamber from a plenum for holding purified fluid. An outlet leads from the plenum to the exterior of the filter vessel.
In conventional practice, on the opposite end of the filters from the tube sheet, separate mount assemblies use compression to secure the filters to the tubes while sealing that end of the tube. Since the mount assemblies contain numerous parts, these parts frequently fall into the filter vessel while disassembling the mount assembly to replace the filters. Parts falling into the vessel must be removed to prevent damage to filter elements caused by motion of the loose parts during service flow, and in nuclear powered generating plants, Nuclear Regulatory Commission oversight mandates the retrieval of the loose parts. Regardless of the application, if loose parts cannot be located and removed with suitable xe2x80x9cfishingxe2x80x9d tools, filter elements must be removed to permit access to the vessel to retrieve the loose parts. U.S. Pat. No. 5,667,679 to Bozenmayer et al. attempts to solve this problem by providing a mount assembly that is removed quickly without losing parts. This design, however, is made of stainless steel parts that are difficult to dispose or recycle when radioactive.
Referring to FIG. 1, another conventional filter vessel 100 has an inlet 102 that delivers unpurified, typically pressurized, fluids to a main chamber 104. The arrows F indicate direction of flow for the fluid during normal operations.
The fluid enters replaceable filter cartridges 106, as known in the art, and through known tubular filters contained thereby that remove unwanted particulate or foreign matter. The purified fluid then flows downward through tubes or pipes 108 that open up into a plenum 110. The plenum is separated from the main chamber 104 by a stainless steel false bottom or tube sheet 112 conventionally welded to the tubes 108. The fluid then exits the filter vessel 100 through an outlet 114. Conventional filter vessels 100 typically vary in diameter from six inches to seven feet (and three foot to eight foot heights) depending on the quantity and size of filter elements contained therein. Vessels are known to accommodate anywhere from two to over 1000 filter cartridges.
Some conventional filter cartridges 106 are held in place by a hold down plate 116 as known in the art. The filter cartridges 106 are single open-ended with a closed top and a protruding bolt, post, rod or other connector 118 to extend upward through a hole in the hold down plate 116 for lateral support and to maintain distances between adjacent filter cartridges. The hold down plates 116 are usually bolted to the perimeter of the vessel or secured to the bottom by long connecting rods (not shown). Either mechanism provides downward force to seal the cartridges 106 to the tube sheet 112. Cartridges 106 that are held down by hold down plates 116 typically have a spigot that fits into holes in the tubesheet 112, and is sealed with either a flat gasket or one or more O-rings (not shown).
Some filter cartridges 106 have threaded bottoms for securing the filter cartridge to the tubesheet 112 and affecting a liquid tight seal, which does not require a hold down plate. However, a steel threaded lower end (not shown) must be rotated numerous times by robot, hand, wrench, other special tool or automatic mechanism to thread each filter cartridge 106 onto one of the tubes 108.
Since a filter cartridge 106 that is threaded requires numerous turns, a worker or mechanism must use a relatively long amount of time to unscrew an old filter cartridge from the end of the tube 108 and then screw a new filter cartridge 106 back onto the tube. When radioactive or hazardous materials are being purified, the longer it takes to replace a filter cartridge, the longer a person or tool is exposed to the dangerous environment. Thus, when special tools are used, frequent replacement is required which is expensive. Alternatively, when a worker is required to replace a filter cartridge by placing his gloved hand in the vessel to turn the filter cartridge, the filter replacement may take a long period of time relative to a safe maximum exposure time available to a single worker. Limited by the maximum safe time periods, changing a filter either requires a number of workers taking turns, which raises labor costs, or requires a single worker to take breaks to reduce the exposure levels obtained in a single period, which is time consuming. Otherwise, the worker may feel encouraged to complete filter replacements within an unsafe period of time.
As shown in FIG. 2, an improvement over the threaded filter cartridge is a guide rod and hook design used to mount a filter cartridge 200 onto a tube 202 welded to a tube sheet 204 such as an Aegis(trademark) Fossil Assembly as is known in the art. The filter cartridge 200 has a guide rod 206 welded to a plate 208 with an end with a hook (as disclosed in U.S. Pat. No. 3,279,608 to Soriente et al.), or in the illustrated case, a rivet 210, to latch on the end of the tube 202. A coil spring 212 and nut 214 are used to seal the top of the filter 216 while compressing the filter cartridge 216 against the tube 202 and to hold it in place against an adapter 218 threaded permanently to the tube 202.
The upper end of the guide rod 206 is used to attach to a positioning lattice (not shown) for lateral stabilization. This design, however, still requires the unthreading of the nut 214 to remove the filter cartridge 200 from the tube 202, and the rivet hook is not considered of adequate strength for high pressure and highly corrosive nuclear power plant applications.
Referring to FIG. 3, in a similar manner as filter cartridge 200, filter cartridge 300 has a guide rod 302 welded to a plate 304. However, the plate 304 has a tubular connector pipe 306 with two opposing holes 308 (only one is shown) that receives a pin (not shown). The pin is permanently press-fit into connector pipe 306 before the filter cartridge 300 is placed on a tubesheet tube 312 within the vessel. Connector pipe 306, with the pin attached, is inserted downward through slots in adapter 310 which is previously attached to the tubesheet tube 312. The connector pipe is pressed downward against tension from a top spring, and is rotated 60 to 90 degrees in either direction to engage cam slots (not shown) on the inside of the adapter 310. The pin is not removed separately, but remains with connector pipe 306 and guide rod 302, and the entire assembly is removed by pressing downward against spring compression and rotating until the pin ends pass upward through the slots in adapter 310.
The top post 314 and mount assembly 316 are also similar to corresponding structures in filter cartridge 200. While this design (named an Aegis(trademark) Nuclear Assembly ) provides two places of contact (two holes) on the tube 312, the pin blocks the interior of the tube 314 reducing the flow cross-section within the tube 312.
Some of the problems of the threaded and guide rod filter cartridges have been addressed by the Ecolock(trademark) system by Graver Technologies. Referring to FIG. 4, the filter cartridge 400 has an adapter 402 threaded to a filter vessel tube (not shown) on a tube sheet (not shown). Prior to placement of the cartridge 400 within the vessel, an extension pipe 404 has an upper end threaded to a filter 406. To place the cartridge 400 within the vessel, a lower end of the extension pipe 404 is inserted over the adapter 402. The extension pipe 404 has a snap ring 408 for securing to a groove on the adapter. The top of the filter 406 has a post 410 for attaching to a positioning lattice (not shown) and aiding in compressing the cartridge 400. A spring assembly 412 is located within the extension pipe 404 for maintaining tension in the filter-to-extension pipe connection and adapter-to-extension pipe connection that further maintains the filter cartridge 400 in place. A passage 414 is provided from the center of the filter 406, through the spring 412, extension pipe 404 and adapter 402, to the filter vessel tube (not shown).
For removal of the Ecolock(trademark) filter cartridge 400, the filter cartridge and associated hardware is rotated 90 degrees, which disengages the snap ring 408 from adapter 402. The spring then assists in ejecting the filter cartridge and hardware assembly in a very expedient manner. However, the Ecolock(trademark) hardware design is very expensive and assembly procedures should include extra measures to ensure that the assembly is in fact locked into place within the vessel since this can be difficult to determine sometimes. If the Ecolock(trademark) assembly is not latched correctly during installation, premature unlatching can occur during operation of the vessel.
Another known filter cartridge and filter vessel eliminates the need for threading the filter cartridge to a tube on a tube sheet. As shown on FIGS. 5A-5D, a filter cartridge 500 has a steel adapter 502 that connects a filter 504 to a stainless steel filter vessel tube 506. As shown in FIGS. 5C-5D, a spring 508 applying forces of 50-60pounds is located between a support ring 510 welded to the exterior of the tube 506 and two pins 512 also welded to the exterior of the tube 506. Referring to FIGS. 5B and 5C, the adapter 502 has two opposing slots 514 (only one shown) for receiving the pins 512 and has an annular groove 516 that slides over the pins as the adapter is rotated about the tube 506. Once the adapter is rotated 90xc2x0 as shown in FIG. 5D, the pins 512 are positioned in two opposing locking apertures 518.
In order to position a filter cartridge 500 on the tube 506, the filter cartridge must be pushed downward (axially) to engage the pins 512 and spring 508, and then rotated a full ninety degrees to place the pins in the locking apertures 518. The spring 508 biases the adapter 502 upward to hold the pins 512 against the bottoms 520 of the locking apertures 518, which further stabilizes and secures the filter cartridge 500 on the tube 506.
In some nuclear power plant filter vessel applications, during backwashing (fluid flow in the upward direction on FIGS. 5A-5D) the spring and fluid can combine to form an axial force of approximately 100 pounds that impacts the filter cartridge 500. The adapter 502 must be made of steel to withstand this force, which is transmitted through the circular pins 512. Otherwise, the high axial forces will cause the pins 512 to rip through an adapter 502 made of a weaker material such as plastic and disengage the filter cartridge 500 during backwashing operations.
Radioactive steel hardware, however, is dangerous, difficult and expensive to handle when replacing filter cartridges. Steel hardware cannot be recycled or incinerated using present technology. If hardware is to be separated and re-used with new filter cartridges, significant operator exposure to radiation occurs during disassembly and re-assembly. For this reason alone, the hardware is often replaced rather than re-used. The discarded hardware that is disposed of as radioactive waste will incur a disposal cost ten times or more its initial cost. Even though certain steels might be reusable after 18 months to six years, usually hardware that is xe2x80x9cburiedxe2x80x9d as radioactive waste remains buried forever.
In keeping with one aspect of the present invention, a coupling device is able to provide a recyclable thermoplastic female coupling on a filter element for engaging a steel male coupling on a fluid conduit by using tabs on the steel male coupling that reduce the impact of forces on the thermoplastic coupling. This is accomplished by spreading out an axial force laterally along flat surface areas of the tabs that engage lands on the female coupling. With this configuration, the tabs impact the lands along a flat surface rather than merely at a single point, which occurs when a cylindrical pin is used as in the known filter adapters.
More specifically, a coupling device for connecting a filter element to a fluid conduit has a male coupling secured to either the fluid conduit or the filter element. The male coupling also has at least two radially projecting tabs. A polymeric female coupling engages with the male coupling for securing the filter element on the fluid conduit. The female coupling also has lands for receiving the tabs. The male and female couplings each have a passageway for fluid that generally defines an axial direction. Each tab is configured for distributing an axial force generally throughout the tab and laterally relative the axial direction so that either the land being forced against the tab or the tab being forced against the land does not damage the female coupling and the filter element remains secured to the fluid conduit
In another aspect of the present invention, a coupling device for connecting a filter element to a fluid conduit has a male coupling with at least two radially extending tabs, and a substantially polymeric female coupling with a land for engaging each tab. The female coupling defines an axis, a circumference and an axially extending access channel continuous with a circumferentially extending land channel receiving one of the tabs. Each land defines a surface of the land channel, and the access channel is configured and disposed on the female coupling so that each access channel receives one tab. Either the access channels are moved axially over the tabs or the tabs are moved axially through the access channels in order to place the tabs within the land channels.
In yet another aspect, a coupling device for connecting a filter element to a fluid conduit has a first coupling with an exterior surface of rotation and at least two tabs projecting generally radially from the exterior surface. The first coupling also defines a passageway for fluid and an axial direction. Each tab has a flat mating surface with a predetermined surface area for distributing an axial force generally throughout the mating surface and laterally relative to the axial direction.
In a further part of the present invention, a female coupling for connecting a fluid element to a fluid conduit has a polymeric body with a land for receiving a projection at a fully secured position. The female coupling defines an axis, a circumference and an axially extending access channel continuous with a circumferentially extending land channel. The land defines a surface of the land channel.
The present invention is also directed to a coupling device for connecting a filter element to a fluid conduit that has a polymeric filter-side coupling attached to the filter element, and a conduit-side coupling attached to the fluid conduit and engaging the filter-side coupling. A selected one of the filter-side coupling and the conduit-side coupling has at least two radially projecting tabs, and the corresponding other coupling has lands for receiving the tabs. The filter-side coupling receives an axial force causing the lands and the tabs to press against each other. The filter-side coupling also has either the lands or the tabs configured for generally distributing the axial force throughout the land or the tab laterally relative to the axial direction so that the filter-side coupling is not damaged by the axial force.
In similar terms, the present invention has a quick-connect coupling device for connecting a filter element to a fluid conduit. The device has a male coupling with generally radially projecting tabs, and a polymeric female coupling with lands for mating with the tabs. One of the couplings is part of the filter element, and the couplings are configured so that they are fully engaged with each other with at most a single twist of a gripping mechanism (robotic mechanism or the like) or human hand grasping the filter element.
The flat tabs also allow for quick placement or removal of the filter element because the tabs merely require a twist of one-sixth of a full 360 degree turn or about 60 degrees, in order to fully secure the couplings or to completely disconnect the couplings. In more detail, a method of rapid installment of a filter element on a fluid conduit has the steps of, with a gripping mechanism or human hand grasping the end of a filter element, moving the filter element axially for engaging a polymeric female coupling on a selected one of the filter element and the fluid conduit with a male coupling on the corresponding opposite one of the filter element and the fluid conduit. One of the couplings is a part of the filter element. Twisting a selected one of the female coupling and the male coupling on the filter element fully engages the fluid conduit coupling without releasing and re-grasping the filter element.